Lichens and industrial pollution - Ecology of Industrial Pollution - page 54

concentrations because levels are much lower than in Europe during its
expansion (LaGreca & Stuzman 2006 ). In Germany, an association between
stemflow concentrations of sulphur and the cover of Lecanora conizaeoides was
identified (Hauck et al. 2001 ). A role for lichen substances through influencing
surface hydrophobicity was also identified (Hauck et al. 2008 ). No single factor
can explain the present day distribution of Lecanora conizaeoides. Buellia pulverea
is associated with Lecanora conizaeoides, and tolerant of both sulphur dioxide
and fluoride pollution. The provenance of these and several other lichens in
anthropogenic habitats is equally unclear. Lecanora vinetorum, a very rare Central
European species known from Switzerland and northern Italy, is a saxicolous
lichen remarkable for having colonized trees and wood sprayed with fungi-
cides containing copper (Laundon 2003 ). It grows on walls, cherry trees
(Prunus avium) and the worked wood of vineyard frames used for the cultivation
of the grape-vine Vitis vinifera (Poelt & Huneck 1969 ; Laundon 2003 ). Lecanora
conizaeoides is most likely to survive on acidic substrates and where local
acidification persists. It is currently growing on acid gravestones in central
London and Edinburgh and occurs in rural areas in similar habitats, as well
as on wood and particular tree species, especially flowering cherry. 'Substrate
switches', where lichens colonise different substrates under changing atmos-
pheric conditions (usually in response to pH changes), have been recorded since
the earliest days of lichen recording (Hawksworth & Rose 1976 ; Seaward 1976 ).

Nitrogen pollution
Over a relatively short time following a reduction in SO 2 emissions, changes in
atmospheric pollutant concentrations across Europe have occurred. Nitrogen
emissions have also changed during the same time period, but these are made
up of several compounds produced from a variety of sources whose effects may
vary with the compound and its source (Wolseley et al. 2006 ). The main sources
of reactive nitrogen in the atmosphere are nitrogen oxides (NO x ) and ammonia
(NH 3 ). Ammonia is largely a product of intensive farming whilst road traffic
contributes a major part of the NO x along with other high temperature com-
bustion processes. Whilst there has been a substantial decline in NO x emissions
since 1990, NH 3 emissions have only decreased slightly (

<

10%) and are still
high especially in agricultural areas (NEGTAP 2001 ; Sutton et al. 2001 ). NH 3
levels have probably increased in urban areas due to catalytic converters (Cape
et al. 2004 ). While nitrogen oxides and their reaction products may be carried
over long distances in the atmosphere in a number of forms, ammonia is
deposited as NH 3 along very local gradients of up to 300m (Fowler et al. 1998 ;
NEGTAP 2001 ; Wolseley et al. 2006 ).
Recorded changes in epiphytic lichen assemblages, initially in the Netherlands
and subsequently across Europe, by independent researchers confirm ammonia
effects on assemblage composition (Van Herk 1999 ;DEFRA 2002 ;Fratiet al. 2007 ;